This invention relates to improvements in a feeding, propelling and tensioning system for tape in a seed-tape manufacturing machine. It may be considered as an improvement on U.S. Pat. No. 3,555,774.
In that patent, as in the present invention, the tape is propelled by a pair of rollers beyond the seed-dispensing station, between which the tape passes. One of these rollers is driven by main drive means while the other roller is an idler urged towards the driven roller. The tape supply is a cylindrical drum that is supported partly by driven peripheral contact means for unwinding the tape from the drum. In this U.S. Pat. No. 3,555,774, an auxiliary drive means acts through a differential to vary the speed of the peripheral contact means, which is driven principally by the main drive means. The differential superimposes a positive or negative speed on the basic speed, as determined by the auxiliary drive means. Control means responsive to the difference in speed at which the tape unwinds relative to the speed of the tape propulsion by the drive rollers, acts to change the speed of the auxiliary drive means and thereby the speed at which the tape unwinds. The control means involves two parallel shafts spaced apart from each other, with the tape passing in tension between them. A pivoted beam supports one of these shafts for movements toward and away from the other shaft according to the length of tape between them by swinging the beam upon its pivot. A cam supported by the beam engages, at times, a plurality of micro-switches, one of which acts to accelerate the auxiliary drive means when the length of tape between the shafts is short enough to tilt the beam to a predetermined amount in one direction, and another microswitch acts to decelerate the auxiliary drive means when the length of tape between the shafts is long enough to cause the beam to tilt a predetermined amount in the opposite direction.
While this device of U.S. Pat. No. 3,555,774 can and does achieve satisfactory results, it has several disadvantages. For one thing, it is expensive to manufacture, because the differential assembly itself is expensive and the arrangement for superimposing the differential's action on the main drive, as applied to the peripheral contact means, calls for a complex and expensive arrangement.
Another difficulty with the embodiment shown in U.S. Pat. No. 3,555,774 is that it tended to induce vibration, due to the use of on/off devices and various mechanical transmission arrangements. Hence, the machine tended to be shaken and thereby its accuracy was impaired to some extent. The action could not be made as smooth as was desired, even though it was used at rapid speeds, and it was more satisfactory at the slower speeds and more accurate when there was less vibration.
The device of U.S. Pat. No. 3,555,774 was at a disadvantage at rapid speeds, when it tended to be inaccurate. It also had the disadvantage that the motor for the main drive was required to do several other things besides operating the main drive and therefore had to be relatively large and expensive, and the transmission arrangements themselves were a requisite of this type of device.